A newly-demonstrated neurohormone released from the corpora cardiaca regulates the synthesis of cytochromes aa8 and/or b during a period of respiratory development in the fat body mitochondria of young adult male Blaberus discoidalis cockroaches. This system constitutes a model for studies on insect neurosecretions and their functions. Knowledge gained from this research will be used to investigate the possibility of disrupting neurosecretory functions or interfering with their actions. The development of the adult fat body is similar in B. discoidalis and in mosquitoes, and regulatory processes on fat body development in B. discoidalis may have a counterpart in mosquitoes. Because of the metabolic significance of the fat body, inhibition of its bioenergetic development would disrupt other adult physiological functions such as reproduction. The action of the neurohormone is well-timed, specific and related to the natural biochemical maturation of the fat body. Preliminary studies show ligated, adult B. discoidalis can be used as a bioassay for the neurohormone based upon the hormone's ability to stimulate the incorporation of (14C)aminolevulinate into cytohemes a+b. Using this bioassay, the following objectives are proposed: (1) isolation of the neurohormone; (2) determination of the action of the hormone on the synthesis of cytohemes a or b (or both); (3) determine whether heme or apoprotein synthesis is the regulated step; and (4) determine the physiological significance of fat body mitochondriogenesis to reproductive capacity in the female.